1. Field of the Invention
This invention relates to bearing lock construction and, more particularly, to an improved bearing lock for confining a bearing within the end bell of a dynamoelectric machine.
2. Description of the Prior Art
In the usual construction of dynamoelectric machines a rotor is secured to a shaft which is journalled for rotation within an annular stator. To properly locate the rotor with respect to the stator, the rotating shaft must be substantially free from radial movement so that a uniform air gap is maintained. In most machines the air gas is very small; therefore, the shaft must be supported by means which will maintain close tolerances.
It has been customary to obtain proper shaft position and close tolerances by the use of "anti-friction" bearings of a type such as a ball bearing which has an inner race, an outer race, and rolling elements therebetween. One such bearing, which carries the thrust load, is mounted in fixed position whereby the bearing inner race is fastened axially on the shaft and the outer race is held axially in the housing. The opposite bearing is fastened axially to the shaft but "floats" in the housing. To assure proper movement, the rotating inner race must have an interference fit on the shaft while the stationary part has a sliding fit with the housing. Normally, electric motors have a revolving shaft upon which the bearings are "pressed" in an interference fit, while the housing fit is loose enough to allow the bearings to be assembled in operating position.
After the thrust load bearing is assembled in operating position, the outer race of the bearing must be secured within its seat in the end bell of the machine housing. Otherwise, the outer race of the bearing will slip and vibrate within its seat as the shaft rotates. This action generates frictional heat or "fretting" corrosion and results in excessive wear of the bearing assembly. In addition, undesirable axial displacement or "end play" of the shaft is prevented when the outer race of the bearing is properly secured in its seat.
Various locking devices are presently employed to confine the bearing assembly within its seat in the machine end bell structure, including end brackets, clamping plates, lock washers and lock nuts, snap rings, stakes, pivotal latching members, and L-shaped locking dogs, all of which must be assembled and tightened prior to installation of the shaft within the end bell. These devices have, in general, proved to be satisfactory in those machines in which preassembly is possible. However, some machines have a structure such as a ventilation fan pressed upon the shaft and lying adjacent to the bearing assembly which prevents preassembly of the locking device. In such machines there is not enough axial clearance between the structure and the end bell to insert, position, and tighten prior art fastening devices against the outer race of the bearing prior to the final assembly.
One existing design which overcomes this problem in part has been suggested by Wulfert U.S. Pat. No. 3,147,050 in which a threaded bearing holding means, disposed in an extended hub portion within which a bearing is seated, engages an outer bearing race along an inclined axis and is accessible through an opening in the housing, thus permitting tightening of the bearing after final assembly of the machine. Since the bearing locking means is carried within a threaded recess of the extended hub portion, the problem of external insertion of a fastening means through an opening of limited clearance is avoided. However, depending upon the configuration of adjacent structure (such as a fan), it may not be possible to engage the threaded bearing holding means as taught by Wulfert. Furthermore, even assuming that such bearing holding means could be engaged and tightened externally, a radial load would be imposed upon the bearing assembly since the bearing holding means is inclined along an acute angle with respect to the shaft axis. This additional radial loading disturbs the preload stability of the bearing assembly, thus decreasing bearing life.
The Irvin U.S. Pat. No. 2,891,829, assigned to the assignee of the present invention, overcomes the objections to Wulfert's device. The locking device taught by Irvin comprises an L-shaped member which is disposed within an end bell portion and is positively guided and retained in bearing locking position. It has minimal projection behind the bearing assembly, thus allowing a structure such as the rotor or fan to be located very close to the bearing assembly without interference. As the locking nut on the threaded end of the L-shaped locking member is torqued, a tang on its opposite end imparts an axially directed force against an outer bearing race, thus holding it securely within its seat without imposing radial loading. The L-shaped locking member, which is carried within the end bell portion, is fixed in a non-interfering position prior to assembly and can be operated from the exterior side of the end bell after the bearing is positioned within its seat. The principal disadvantage of the locking device of Irvin is that, although guiding means are provided, it is possible to draw the locking member against the end bell instead of the outer race of the bearing. This condition has been found to occur when the locking member is torqued and vaulted over a first stop and is subsequently rotated away from the bearing race until it engages a second stop, thereby completely overlying an end bell portion instead of the outer race of the bearing. Such a condition would remain undetected since the locking operation is not visible from the exterior of the machine. A second disadvantage of the locking device of Irvin is that it can only be installed or removed when the end bell is disassembled from the machine; that is, it cannot be inserted into or withdrawn from the end bell after the machine has been completely assembled. The usual procedures of testing, disassembly, repair or adjustment, and reassembly of the machine could obviously be performed more easily and rapidly if the locking means could be inserted, positioned, and secured from the machine exterior after final assembly and testing.
It is, therefore, desirable to provide a simple bearing confining means which can be inserted or removed from the exterior of the machine without requiring disassembly of the end bell. Such locking means should have minimal axial projection so as to avoid interference with adjacent structure. Furthermore, the locking means should not impose radial loading upon the bearing assembly or disturb the radial preloading of the bearing assembly in any way. Finally, positive guiding means should be provided to insure that the locking means will only engage the bearing outer race. The invention described herein accomplishes these desired objects.